The Pentagon told U.S. lawmakers this week it will likely take six months to clear the mines set in the Strait of Hormuz, The Associated Press reported, citing a person familiar with the situation who was granted anonymity to discuss the sensitive information.

Officials from the U.S. Department of Defense delivered the information during a classified briefing at the House Armed Services Committee on Tuesday, according to the report.

The session left more questions than answers as lawmakers probed for information about the cost of the war against Iran, the strategy and objectives, the person told AP. The lawmakers also raised questions that have still gone unanswered about the strike on a school compound during the early days of the Iran war.

The Washington Post, citing three officials speaking on the condition of anonymity, reported that lawmakers were told that Iran may have emplaced 20 or more mines in and around the Strait of Hormuz, the vital waterway for the movement of Middle Eastern oil through the Persian Gulf.

Some were floated remotely using GPS technology, which has made it difficult for U.S. forces to detect the mines as they are deployed, the senior defense official told lawmakers. Others are believed to have been laid by Iranian forces using small boats.